For example, Patent Documents 1 and 2 disclose a heat sink arranged under a floor of a railway vehicle and used for cooling a power converter for driving the vehicle. The heat sink includes a base to which a power semiconductor device which is a heating element is attached, and a heat dissipating portion having a plurality of fins each vertically arranged on the base. The heat sink is exposed to a traveling air stream generated while the vehicle travels, and therefore heat of the power semiconductor device is dissipated by heat transfer through each of the fins.